402 SHIGEYUKI KOMINE 



opposite direction — as was found between these two series at 

 two hours after feeding. Soon after the content of non-protein 

 nitrogen of the test brain has reached a minimum, at about 

 eight or nine hours, the value begins to increase again, and 

 finally at twenty-three hours after feeding the value for the non- 

 protein nitrogen reaches once more the original level for the con- 

 trol rats. 



The sort of variation just described was enth-ely unexpected, 

 although an increase immediately after feeding and a diminution 

 later were anticipated. The form of the graph at once indicates 

 the periodic nature of the alteration in the content of non-protein 

 nitrogen during the interval chosen. This periodic variation in 

 the non-protein nitrogen content must of course be interpreted. 

 It is evident that for a satisfactory understanding of this inter- 

 esting phenomenon we must further analyze the non-protein 

 nitrogen into its components, such as amino acids, urea, am- 

 monia, creatinine, etc., as such a determination would reveal 

 what sort of nitrogen was actually responsible for the variations 

 shown by the graph. Although I have not as yet made an 

 analysis of this kind, yet from the data given by numerous 

 investigators, I feel justified in suggesting the following general 

 interpretation. 



The metabolic products from the digestive tract, which have 

 been absorbed and then carried by the circulation, are reab- 

 sorbed from the blood by the brain tissue until this is saturated 

 to a maximum degree with these metabolites. 



In support of this view, there are abundant experimental data 

 which show a quick absorption by the organs and tissues of 

 non-protein substances injected into the circulation. For in- 

 stance, Folin and Denis ('12) always obtained an increase in the 

 non-protein nitrogen of muscle of the cat following the injection 

 of amino acids, amino-acid digestion mixture, or Witte's pep- 

 tone, into a ligated loop of intestine. Van Slyke and Meyer 

 ('13-'14), by the now standard nitrous method, found an in- 

 crease of amino acids in the muscles and several visceral organs 

 of dogs after the injection into the venous blood of amino a^ids 

 and protein digestion mixtures. Van Slyke and Meyer came to 



